Product Reference - Oriental Motor

Technical Reference
Stepping Motors
■Structure of Stepping Motors
The figures below show two cross-sections of a 5-phase stepping
motor.
The stepping motor consists primarily of two parts: a stator and
rotor.
The rotor is made up of three components: rotor 1, rotor 2 and a
permanent magnet. The rotor is magnetized in the axial direction so
that, for example, if rotor 1 is polarized north, rotor 2 will be polarized
south.
Ball Bearing
Rotor 1
Permanent Magnet
Rotor 2
■Stepping Motor's Principle of Operation
Following is an explanation of the relationship between the
magnetized stator small teeth and rotor small teeth.
●When Phase "A" is Excited
When phase A is excited, its poles are polarized south. This attracts
the teeth of rotor 1, which are polarized north, while repelling the
teeth of rotor 2, which are polarized south. Therefore, the forces on
the entire unit in equilibrium hold the rotor stationary. At this time,
the teeth of the phase B poles, which are not excited, are misaligned
with the south-polarized teeth of rotor 2 so that they are offset 0.72˚.
This summarizes the relationship between the stator teeth and rotor
teeth with phase A excited.
No Offset
3.6°
0.72°
3.6°+0.72°
N
S
N
Stator
N
Phase A Phase B
7.2°
Shaft
Stator
Winding
Motor Structural Diagram: Cross-Section Parallel to Shaft
The stator has ten magnetic poles with small teeth, each pole being
provided with a winding.
Each winding is connected to the winding of the opposite pole so
that both poles are magnetized in the same polarity when current is
sent through the pair of windings. (Running a current through a given
winding magnetizes the opposing pair of poles in the same polarity,
i.e., north or south.)
The opposing pair of poles constitutes one phase. Since there are
five phases, A through E, the motor is called a "5-phase stepping
motor."
There are 50 small teeth on the outer perimeter of each rotor, with
the small teeth of rotor 1 and rotor 2 being mechanically offset from
each other by half a tooth pitch.
Rotor 1
N
No Offset
Phase C
Phase D
Current
Phase E
●When Phase "B" is Excited
When excitation switches from phase A to B, the phase B poles are
polarized north, attracting the south polarity of rotor 2 and repelling
the north polarity of rotor 1.
0.72°
N
N
S
S
N
3.6°
S S
N
S
Excitation: To send current through a motor winding
Magnetic pole: A projected part of the stator, magnetized by excitation
Small teeth: The teeth on the rotor and stator
Phase A
Shaft
Stator
Rotor
Phase B
Phase A
Rotor 1
N
Phase B
Stator
Phase C
Phase D
N
0.72°
Phase C
S
S
N
Current
Phase E
3.6°
S S
Phase D
N
Phase E
Motor Structural Diagram: Cross-Section Perpendicular to Shaft
F-46 ORIENTAL MOTOR GENERAL CATALOG 2009/2010